Polyurethanes are prepared by reacting a compound which contains at least two reactive hydrogen atoms with a polyisocyanate. The active hydrogen-containing compound is typically a polyether or polyester polyol, but may also be a polyamine containing primary or secondary amino functionalities produced by replacing the hydroxyl functionalities of a polyol with amino groups. Both the active hydrogen-containing compound and the polyisocyanate contain at least two reactive functionalities. The polyisocyanate is generally employed in a slight molar excess relative to the total amount of the active hydrogen-containing materials in the composition. By appropriate selection of the particular active hydrogen-containing materials and the particular polyisocyanates, polymers having a wide variety of properties may be produced.
The range of properties of the resultant polymers may be extended by including in the reaction mixture one or more additional active hydrogen-containing compounds, which are generally referred to in the art as "chain extenders." Chain extenders are isocyanate-reactive materials possessing at least two active hydrogen atoms, and having molecular weights generally less than about 400. The reactive functional groups of chain extenders are generally primary or secondary hydroxyl groups, or primary or secondary amines.
Chain extenders containing hydroxyl groups are frequently somewhat slow to react with the polyisocyanate, and require one or more catalysts to achieve a sufficiently fast reaction. Such catalysts are typically organometallics such as dibutyl tin dilaurate and other similar materials known to those skilled in the art.
The residues of metal-containing catalysts can cause thermal instability in the ultimate polymer. Another potential difficulty with hydroxyl-containing chain extenders is that some of these have a limited solubility in the polyol employed as the primary active hydrogen-containing compound of the composition, thus limiting the amount of chain extender which can be used in the formulation.
Amine-containing chain extenders generally react more rapidly than the corresponding hydroxyl-containing materials, but sometimes react too fast, and in addition, may impart an odor to the resultant polymeric product.
Typical chain extenders known to the art are compounds such as ethylene glycol, 1,4-butanediol, diethylene glycol, ethylenediamine, hydrazine, isophoronediamine, diethyltoluenediamine, and methylene-bis(orthochloroaniline). Such chain extenders find application not only in the field of polyurethane and polyurea chemistry, but also in various other polymeric systems such as epoxides and polyamides, for example.
Diamines such as dipiperazinyl urea and 1,2-bis(piperazinyl)ethanedione have been reported to be useful for the preparation of certain pharmaceutical materials, but have not apparently been suggested as chain extenders in polymeric systems. See Derwent Abstract 86-248748/38.
It is understood by those skilled in the art that the reaction between a polyol and a polyisocyanate produces a polyurethane, a reaction between a polyamine and a polyisocyanate produces a polyurea, and a reaction involving a polyol, a polyisocyanate, and a polyamine chain extender produces a poly(urethane/urea).
The art is always interested in finding new chain extender materials which possess adequate reactivity with polyisocyanate and produce polymers having good physical properties, in particular, improved hardness and modulus. Such new chain extenders are the subject of the present application.